Threaded joint



THREADED JOINT Filed Dec. 29, 1958 2 Sheets-Sheet 1 & INVENTOR.

Jude 1a, 1940. M, FRAM 2,204,754

THREADED JOINT Filed Dec. 29, 1938 2 Sheets-Sheet Z INVENTOR.

B 45 1 10. vfigpk 4A., ATTORNEYS.

Patented June 18, 1946 UNITED STATES PATENT OFFICE THREADED JOINT i William M. Frame, Ben Avon, Pa., assignor to The National Supply Company, Pittsburgh, Pa., a

corporation of Pennsylvania Application December 29, 1938, Serial No. 248,278

3 Claims.

This invention relates to threaded joints, and

more particularly is concerned with threaded joints for oil well casing of a character adapted for use with a circumferentially extending seall ow joint efiiciency. Furthermore, standard threaded casing joints usually must be made up with a lubricant which gasifies during a subsequent welding operation and blows through the 5 ing medium, such as a ring of welding metal. weld seemingly in spite of every precaution that 5 In recent years a serious efiort has been made can be taken. to eliminate the usual threaded joint connecting It is the general object of my invention to oil Well casing together end to end and to weld provide a threaded oil well casing joint particthe casing lengths together. These efforts have ularly adapted to be used in conjunction witha met with some success in shallow wells, but circumferentially continuous seal of welding ma- 10 welding casing down the. hole has not been acterial or the like. cepted by the trade for deep wells because of Other and more specific objects of my inventhe-danger of weld failure with the attending tion include the provision of a threaded joint complications. A standard type of joint used for oil well casing or the like which has a relin welding casing down the hole comprises a ,atively high efliciency (ultimate strength of joint 15 bell and spigot joint in which the bell is formed divided by ultimate strength of member con on the upper end of each casing length and the nected equals joint efiiciency in per cent), can spigot is formed on the lower end. After stabbe shipped without protectors, can be made up bing the spigot end into the bell, an endless ring with little or no lubricant, and which can be of welding metalis laid around the joint bep o u inexpensively by a d production 20 tween the end of the bell and the adjacent porequipment with broad working tolerances. tion of the spigot. It has been found in order Another object of my invention includes the to provide the necessary strength in axial pull p ovision of a t d d joint for Oil Well Casing and the requisite seal that two or three layers or the like which can be cut on a relatively thin of welding material must be laid around the joint. pipe end W i e maintaining a maximum of baek- 25 Further, even the most skillful welder finds ng ta n Which can be readily Stabbed great difficulty in making the weld sufficiently ing e assembly of the joint. free of strain so that the joint efiiciency is high Another object of my invention is to provide and the seal is perfect under the various com a threaded joint to be used in conjunction with a ditions to which the joint is subjected. circumferential ring of sealing material and in 30 In Howard G. Texterscopending application, which the threaded J'O n and 110i? the-Seal acts Serial No. 247,756, filed December 27, 1938, now to take up any b ndin s ss s on the j nt u Patent No. 2,187,798, dated January 23, 1940, without the necessary structure interfering with there is disclosed and claimed a combined welded t e rapidity and e se With which my joint can 5 and threaded joint and a method of making it be assembled. which avoids and overcomes the foregoing and The foregoing and other objects of my invenother difiiculties of known practices. However, tion are achieved by the provision of a threaded standard threaded joints for connecting oil well joint for oil well casing or the like in which comcasing are not adapted for use with the Texter plementary e and female J' members are invention. First, standard threaded casing provided with complem a y eads having 40 40 joints are relatively expensive and necessitate substantially fia Crests and roots po n d close production tolerances. Moreover, the parallel to the joint XiS- e Complementary standard American Petroleum Institute joint threads are formed with substantially-flat flanks employs a v or Briggs thread so that when the having an incl d d n l f w n about zero joint is subjected to axial pull the sharply tadegrees and about eighteen degrees and the roots 5 D pered flanks of the threads act in wedging reof the female thread at the small or pipe end lation on each other and cause radial expansion thereof are defined by tapers for somewhat less of the female joint member and radial contracthan half of the thread length and the roots tion of the male joint member. This movement, so defined receive the crests of the male thread together with attendant relative longitudinal in bottoming relation. The roots on the large 50 movement tends to subject the welding metal to excessive stresses. Again, substantially all standard threads must be protected with guards during shipment or other handling" and the A. P. I. joint is open to the additional objection of or pipe end of the male thread are defined by a taper for somewhat less than half of the thread length, and the rootsso defined receive the crests of the female thread in bottoming relation. Preferably my improved joint includes 5 of the joint.

complementary threads having crests of a constant width and roots of progressively greater width outwardly of the center of the thread so as to provide a clearance between the flanks of the threads which is progressively greater outwardly of the center of the thread.

For a better understanding of my invention reference should be had to the accompanying drawings in which Fig. 1 is a side elevation partly in section of an improved joint incorporating the principles of my invention; Fig. 2 is a diagrammatic view of the thread illustrated in Fig. 1; and Fig. 3 is a cross sectional view on an enlarged scale of the thread form shown in Figs. 1 and 2.

While the improved threaded joint of my invention can be employed for threaded joints of various kinds. it is particularly adapted for use in connecting oil well casing together end to end with a subsequent welding operation, and accordingly has been so illustrated and will be so described.

The form and construction of my improved thread will best be understood from Fig. 2. in which the number of threads in a typical joint has been reduced and the height thereof increased to better indicate the construction. In this figure of the drawings, the numeral ID indicates a female joint member which is provided with a continuous helical thread l2. Received within the female joint member I0 is a male joint member H which is formed with a continuous helical thread l6 which is complementary to the thread l2. The threads l2 and I6 are of a modified Acme type and include flat crests and roots which are parallel to the axis The sides of flanks of the threads are substantially fiat and are formed on an included angle of between approximately zero degrees and approximately eighteen degrees, and generally the included angle is about twelve degrees.

The roots of the thread Hi from the end of the male member to a radialplane l8, which is positioned somewhat more than half the length of the thread from the end of the male member, are defined by a cylindrical surface 20. From the plane I8 to the pipe or large end of the male joint member H the roots of the male thread l6 are defined by a truncated conical surface 22. The roots of the thread l2 of the female joint member ID are defined from a radial plane 24, to the large or open end of the female member l0 by a cylindrical surface 26. The radial plane 24 is positioned somewhat more than half the length of the thread from the end of the female member. The roots of the thread l2 of the joint member ID are defined by a truncated conical surface 28 from the radial plane 24 to the pipe or small end of the female joint member It).

The crests of the thread l6 from the small end of the male joint member H to the radial plane 24 are likewise defined by the conical surface 28 so that they bottom in the roots of the complementary female member in this portion of the thread length. However, as shown in the drawings the crests of the opposed female thread from the radial plane 24 to the small or pipe end of the female joint member ID do not bottom in the opposed complementary roots of the male member. In a similar, but reversed manner, the crests of the female thread 12 from the radial plane I8 to the open or large end of the female joint member I0 are defined by the truncated conical surface 22 so that these crests bottom in the opposed roots of the thread IS on the male joint member I4. However, the crests of the thread IS on the male member N do not bottom in the opposed roots of the female thread between the radial plane l8 and thelarge or open end of the female joint member IU. As shown in Fig. 2, none of the crests of the threads l2 and 18 bottom in the opposed roots of the threads between the radial planes l8 and 24.

While the exact number of threads per inch, the thread height and width and the tapers of the truncated conical surfaces 22 and 28 can be widely varied while maintaining many of the advantages of my invention. it will be understood that these various figures are largely dependent.

upon the particular use to which my improved threaded joint is to be put. By way of example, in an oil well casing joint formed directly on the ends of a seamless oil well casing having a five inch inside diameter, and a five and a inch outside diameter, I employ five threads per inch. each approximately /10 of an inch in width and "Hum of an inch in height. The taper of the truncated conical surfaces 22 and 28 is between approximately of an inch and approximately 1 3/ of an inch per foot, and generally is at about 1 /4 of an inch per foot.

An important feature of my improved threaded joint is that of forming all of the crests of the threads on both the male and female joint members of equal width, as'shown'in the drawings. When this is done the roots of the opposed complementary threads are formed of progressively increasing width outwardly of the planes l8 and 2%. This not only facilitats the manufacture of the thread chasers used to cut the thread. but also results in gradually increased flank clearances outwardly of the radial planes l8 and 24 on the thread. This progressively greater flank clearance is clearly shown in Fig. 2 of the drawings, and I have found results in a more uniform loading of the threads when the joint is subjected to axial load. In other words. the threads at the center of the joint, for example, those between the radial planes l8 and 24, have their flank portions engaged first when the joint is subjected to axial load, and thereafter as the load is built up on the joint each of the flanks of the remaining threads comes into engagement upon the deformation of the threads of the joint which first engage so that all of the individual thread convolutions are loaded when the joint is subjected to relatively high axial tension. Without the progressively greater flank clearance outwardly of the center of the joint the center threads in the joint are not subjected to as great a load as the threads near the ends of the joint and thread failure or permanent deformation may result.

The threaded joint shown diagrammatically in Fig. 2 has been illustrated in the made-up position but with the weight of the male joint member I4 being downwardly against the female joint member I0. On the other hand, the threaded joint shown in Fig. 1 has been illustrated with the individual threads of the joint in the position that they take when the joint is subjected to an axially applied tensile load so that the flank clearances shown in Fig. l are with the various parts of the joint stretched to bring the flank surfaces into load-carrying engagement in quite a different relation than that shown in Fig. 2. However, it should be understood that the various flank clearances shown in both Figs. 1 and 2 are half exaggerated to better illustrate the principle of my invention.

The female member ID is shown in Fig. l as comprising a belled end formed integral with a length of conduit, such as a casing. However, it should be understood that the female member can be formed in any known manner as by upsetting, or it may take the form of a coupling sleeve or a female joint member out directly on a length of pipe, although neither of the last two forms is preferable.

From the foregoing it will be evident that the objects of my invention have been achieved by the provision of an improved joint for oil well casing or the like and including complementary strong, rough threads which are relatively simple in construction but which provide a joint particularly adapted to resist relatively heavy axially applied tensile stresses. The improved joint of my invention is readily cut in large scale production quantities on a standard screw-cutting lathe to effect a satisfactory product with broad working tolerances. The joint does not have to be guarded by protectors during shipment and can be readily made up with little or no lubricant. The threads bottoming at both ends of the joint not only hold the parts aligned for welding but absorb any bending stresses on the joint in use. The clearance of the threads at the center of the joint allows the joint to be assembled and almost fully made up without the use of tongs. Furthermore, the sharply tapered runout of the threads insures easy stabbing and the cylindrical body of the thread provides a maximum of strength on relatively thin-walled pipes or the like.

It will be understood that my improved joint is particularly adapted to be used in conjunction with a ring of welded-on or other sealing material, all as particularly described and claimed in Howard G. Texters said Patent No. 2,187,798, dated January 23, 1940. My improved thread is particularly strong in axial tension due to the progressive loading ofthe individual thread convolutions, all as described and claimed in my pending application Serial No. 247,782, filed December 27, 1938, now Patent No. 2,183,644, dated December 19, 1939.

While in accordance with the patent statutes I have specifically illustrated and described one embodiment of my invention, it should be understood that I am not to be limited thereto or thereby but that my invention is defined in the appended claims.

I claim:

1. A threaded joint for thin walled oil well casing and the like and comprising male and female joint members formed with complementary threads of a modified Acme type thereon, the roots of the female thread at the small or pipe end thereof being defined by a taper and receiving the crests of the male thread in'bottoming relation, the roots on the large or pipe end of the male thread being defined by a taper and receiving the crests of the female thread in bottoming relation, said bottoming extending inwardly from each end for at least one-fifth but less than half of the total thread length so as to provide a rigid joint, and the intermediate .thread crests and roots being defined by substantially cylindri-' cal surfaces, none of said intermediate crests bottoming in opposed roots.

2. A threaded joint for thin walled oil well casing and the like and comprising male and female joint members formed with complementary threads of a modified Acme type thereon, the roots of the female thread at the small or' pipe end thereof being defined by a taper for less than half of the thread length and receiving the crests of the male thread in bottoming relation, the roots on the large or pipe end of the male thread being defined by a taper for less than half of the thread length and receiving the crests of the female thread in bottoming relation, the crests of those portions of the threads having taper-defined roots being defined by cylinders, and the remaining thread crests and roots being defined by substantially cylindrical surfaces, none of said remaining crests bottoming in opposed roots.

3. A threaded joint for thin walled oil well casing and the like and comprising male and female joint members formed with complementary threads of a modified Acme type thereon, the roots of the female thread at the small or pipe end thereof being defined by a taper for less than half of the thread length and receiving the crests of the male thread in bottoming relation, the roots on the large or pipe end of the male thread .being defined by a taper for less than half of the thread length and receiving the crests of the female thread in bottoming relation, and the intermediate thread crests and roots being defined by, substantially cylindrical surfaces, none of said intermediate crests bottoming in opposed roots, said thread convolutions defined in part by the tapers having progressively greater flank clearances outwardly to the ends of the threads.

WILLIAM M. FRAME. 

